Programmable resistive memory cell with sacrificial metal

ABSTRACT

Programmable metallization memory cells include an electrochemically active electrode and an inert electrode and an ion conductor solid electrolyte material between the electrochemically active electrode and the inert electrode. A sacrificial metal is disposed between the electrochemically active electrode and the inert electrode. The sacrificial metal has a more negative standard electrode potential than the filament forming metal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/500,899 filed Jul. 10, 2009 which claims the benefit of U.S.Provisional Application No. 61/109,583 filed Oct. 30, 2008, the contentsof which is hereby incorporated by reference in its entirety.

BACKGROUND

Memory devices are common in electronic systems and computers to storedata. These memory devices may be volatile memory, where the stored datais lost if the power source is disconnected or removed, or non-volatile,where the stored data is retained even during power interruption. Anexample of a non-volatile memory device is a programmable metallizationcell (PMC).

A PMC utilizes a fast ion conductor such as a chalcogenide-type or anoxide-type (e.g., NiO) and at least two electrodes (e.g., an anode and acathode) with the fast ion conductor between the electrodes. When avoltage is applied across the electrodes, superionic clusters orconducting filaments rapidly grow from the cathode through the fast ionconductor towards the anode. When the clusters or filaments are present,the cell is in a low resistance state. When an electric field ofopposite polarity is applied across the electrodes, the conductingfilaments dissolve and the conducing paths are disrupted, providing thecell with a high resistance state. The two resistance states areswitchable by the application of the appropriate electric field and areused to store the memory data bit of “1” or “0”.

While a high ionic conductive solid electrolyte (e.g., chalcogenide)provides a high speed switch between the two resistance states of thePMC, this material can suffer from poor data state retention. Anotherlower ionic conductive solid electrolyte (e.g., oxide electrolyte)provides for good data state retention, but this material can sufferfrom slow switching between the two resistance states of the PMC. Thus,there is a tradeoff between switching speed and data retention in a PMCcell depending on what solid electrolyte (in regards to the materialproperty differences) is provided in the PMC cell. There is a need for aPMC cell that can provide both fast switching speeds and extended dataretention.

BRIEF SUMMARY

The present disclosure relates to programmable metallization memorycells having sacrificial metal that has a more negative standardelectrode potential than the filament forming metal. The sacrificialmetal can donate electrons to the filament forming metal in the lowresistance state of the programmable metallization memory cell tostabilize the low resistance state of the programmable metallizationmemory cell and improve the data retention of the programmablemetallization memory cell.

In one illustrative embodiment, a programmable metallization memory cellincludes an electrochemically active electrode and an inert electrodeand an ion conductor solid electrolyte material between theelectrochemically active electrode and the inert electrode. Asacrificial metal is disposed between the electrochemically activeelectrode and the inert electrode. The sacrificial metal has a morenegative standard electrode potential than the filament forming metal.

These and various other features and advantages will be apparent from areading of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIG. 1 is a schematic side view diagram of an illustrative programmablemetallization memory cell having a sacrificial metal layer;

FIG. 2 is a schematic side view diagram of an illustrative programmablemetallization memory cell having a sacrificial metal particles;

FIG. 3A is a schematic side view diagram of an illustrative programmablemetallization memory cell in a low resistance state;

FIG. 3B is schematic side view diagram of the illustrative programmablemetallization memory cell in a high resistance state;

FIG. 4 is a schematic diagram of an illustrative programmablemetallization memory unit including a semiconductor transistor;

FIG. 5 is a schematic diagram of an illustrative programmablemetallization memory array;

FIG. 6 is a flow diagram of an illustrative method of forming aprogrammable metallization memory cell with sacrificial metal;

FIGS. 7A-7C are schematic cross-section views of another programmablemetallization memory cell with oxide layer at various stages ofmanufacture.

FIG. 8 is a flow diagram of another illustrative method of forming aprogrammable metallization memory cell with sacrificial metal; and

FIGS. 9A-9B are schematic cross-section views of another programmablemetallization memory cell with oxide layer at various stages ofmanufacture.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying setof drawings that form a part hereof and in which are shown by way ofillustration several specific embodiments. It is to be understood thatother embodiments are contemplated and may be made without departingfrom the scope or spirit of the present disclosure. The followingdetailed description, therefore, is not to be taken in a limiting sense.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

Spatially related terms, including but not limited to, “lower”, “upper”,“beneath”, “below”, “above”, and “on top”, if used herein, are utilizedfor ease of description to describe spatial relationships of anelement(s) to another. Such spatially related terms encompass differentorientations of the device in use or operation in addition to theparticular orientations depicted in the figures and described herein.For example, if a cell depicted in the figures is turned over or flippedover, portions previously described as below or beneath other elementswould then be above those other elements.

As used herein, when an element, component or layer for example isdescribed as being “on” “connected to”, “coupled with” or “in contactwith” another element, component or layer, it can be directly on,directly connected to, directly coupled with, in direct contact with, orintervening elements, components or layers may be on, connected, coupledor in contact with the particular element, component or layer, forexample. When an element, component or layer for example is referred toas begin “directly on”, “directly connected to”, “directly coupledwith”, or “directly in contact with” another element, there are nointervening elements, components or layers for example.

The present disclosure relates to programmable metallization memorycells having sacrificial metal that has a more negative standardelectrode potential than the filament forming metal. The sacrificialmetal can donate electrons to the filament forming metal in the lowresistance state of the programmable metallization memory cell tostabilize the low resistance state of the programmable metallizationmemory cell and improve the data retention of the programmablemetallization memory cell. While the present disclosure is not solimited, an appreciation of various aspects of the disclosure will begained through a discussion of the examples provided below.

FIG. 1 is a schematic side view diagram of an illustrative programmablemetallization memory cell 10 having a sacrificial metal layer 15. Memorycell 10 includes an electrochemically inert electrode 12, anelectrochemically active electrode 14, and an ion conductor solidelectrolyte material 16. The ion conductor solid electrolyte material 16is between the electrochemically inert electrode 12 and theelectrochemically active electrode 14. A sacrificial metal 15 isdisposed between the electrochemically active electrode 14 and the inertelectrode 12. The sacrificial metal 15 has a more negative standardelectrode potential than the filament forming metal forming theelectrochemically active electrode 14.

In many embodiments, the programmable metallization memory cell 10 isconstructed with a sacrificial metal layer 15 disposed on either theelectrochemically active electrode 14 and the inert electrode 12. Thesacrificial metal 15 can have a smaller atomic radius than the filamentforming metal forming the electrochemically active electrode 14. In manyembodiments, the filament forming metal 14 is silver and the sacrificialmetal 15 is nickel, chromium or zinc, for example.

As described below, the sacrificial metal 15 donates electrons to thefilament forming metal 14 to stabilize filaments formed by the filamentforming metal 14 when the programmable metallization memory cell 10 isin the low resistance state. The sacrificial metal layer 15 is depositedthin enough so it does not participate in the formation of the filamentsformed by the filament forming metal 14 when the programmablemetallization memory cell 10 is in the low resistance state. In manyembodiments the sacrificial metal layer 15 has a thickness of less than50 nanometers, or less than 40 nanometers, or less than 30 nanometers.

The electrochemically active electrode 14 can be formed of any usefulelectrochemically active material such as, silver (Ag) or copper (Cu).The active electrode 14 can have any useful thickness, for example, from50 Angstroms to 5000 Angstroms. In many embodiments the active electrode14 has a greater thickness than the sacrificial metal layer 15. A topelectrode (not shown) can be disposed on the electrochemically activeelectrode 14. The top electrode can be formed of any usefulelectrochemically inert metallic material, as described below.

The inert electrode 12 can be formed of any useful electrochemicallyinert metallic material. In many embodiments, the inert electrode 12 isformed of electrochemically inert metal such as, tungsten (W), nickel(Ni), molybdenum (Mo), platinum (Pt), gold (Au), palladium (Pd), andrhodium (Rh) for example. In some embodiments the inert electrode 12 hastwo or more metal layers, where the metal layer closest to the ionconductor solid electrolyte material 16 is electrochemically inert whileadditional layers can be electrochemically active. The inert electrode12 can also be referred to as a bottom electrode. The inert electrode 12can be, but need not be formed on a substrate. The substrate, ifutilized, can include silicon, a mixture of silicon and germanium, andother similar materials. FIG. 1 and FIG. 2 does not depict an optionalsubstrate.

The ion conductor solid electrolyte material 16 can be formed of anyuseful material that provides for the formation of conducting filaments18 within the ion conductor solid electrolyte material and extendbetween the electrochemically active electrode 14 and the inert metalcontact 12 upon application of an electric field EF+. In manyembodiments the ion conductor solid electrolyte material 16 is achalcogenide-type material such as, for example, GeS₂, GeSe₂, CuS₂,CuTe, and the like. In other embodiments the ion conductor solidelectrolyte material 16 is an oxide-type material such as, for example,WO₃, SiO₂, Gd₂O₃ and the like.

FIG. 2 is a schematic side view diagram of an illustrative programmablemetallization memory cell 10 having a sacrificial metal particles 15.Memory cell 10 includes an electrochemically inert electrode 12, anelectrochemically active electrode 14, and an ion conductor solidelectrolyte material 16, as described above. Sacrificial metal 15particles are dispersed within the ion conductor solid electrolytematerial 16. The sacrificial metal 15 particles have a more negativestandard electrode potential than the filament forming metal forming theelectrochemically active electrode 14. The sacrificial metal 15particles can have a smaller atomic radius than the filament formingmetal forming the electrochemically active electrode 14. In manyembodiments, the filament forming metal 14 is silver and the sacrificialmetal 15 is nickel, chromium or zinc, for example.

As described below, the sacrificial metal 15 particles donate electronsto the filament forming metal 14 to stabilize filaments formed by thefilament forming metal 14 when the programmable metallization memorycell 10 is in the low resistance state. The sacrificial metal 15particles are co-deposited with the ion conductor solid electrolytematerial 16 at a concentration that is low enough so it does notparticipate in the formation of the filaments formed by the filamentforming metal 14 when the programmable metallization memory cell 10 isin the low resistance state.

FIGS. 3A and 3B are cross-sectional schematic diagrams of anillustrative programmable metallization memory cell 10. In FIG. 3A,memory cell 10 is in the low resistance state. In FIG. 3B, cell 10 is inthe high resistance state. Programmable metallization cell (PMC) memoryis based on the physical re-location of superionic regions and formingconducting filaments 18 within an ion conductor solid electrolytematerial 16.

Application of an electric field EF+ across the electrochemically activeelectrode 14 and the inert metal contact 12 allow metal cations (i.e.,silver ions) to migrate toward the inert metal contact 12, electricallyconnecting the inert metal contact 12 to the electrochemically activeelectrode 14. This electrical connection gives rise to the lowresistance state of the programmable metallization memory cell 10.

Reading the PMC 10 simply requires a small voltage applied across thecell. If the conducting filaments 18 electrically connect the inertmetal contact 12 to the electrochemically active electrode 14, theresistance will be low, leading to higher current, which can be read asa “1”. If conducting filaments 18 do not electrically connect the inertmetal contact 12 to the electrochemically active electrode 18, theresistance is higher, leading to low current, which can be read as a “0”as illustrated in FIG. 3B.

When the external bias or electric field EF+ is removed, the conductingfilaments 18 tend to disintegrate into ions (e.g., silver ions) andstart to retreat back to the anode or disperse into the ion conductorsolid electrolyte material 16. The sacrificial metal 15 has a morenegative standard potential than the metal forming the conductingfilaments 18, thus electrons will flow from the sacrificial metal 15 tothe conducting filaments 18 to stabilize the conducting filaments 18 andthereby improving the low resistance data state retention. In this lowresistance state, after donating the electrons, the sacrificial metal isin the ionic state 15A in ion conductor solid electrolyte material 16.

FIG. 3B is schematic diagram of an illustrative programmablemetallization memory cell 10 in a high resistance state. Application ofan electric field of opposite polarity FE− ionizes the conductingfilaments 18 and dissolves ions from the electrically conductingfilaments 18 back to the electrochemically active electrode 14, breakingthe electrical connection between the inert metal contact 12 to theelectrochemically active electrode 14 and gives rise to the highresistance state of the programmable metallization memory cell 10. Thesacrificial metal ions 15A move toward the negative charged anode andreduce into the metallic state. The low resistance state and the highresistance state are switchable with an applied electric field and areused to store the memory bit “1” and “0”.

FIG. 4 is a schematic diagram of an illustrative programmablemetallization memory unit 20 including a semiconductor transistor 22.Memory unit 20 includes a programmable metallization memory cell 10, asdescribed herein, electrically coupled to semiconductor transistor 22via an electrically conducting element 24. Transistor 22 includes asemiconductor substrate 21 having doped regions (e.g., illustrated asn-doped regions) and a channel region (e.g., illustrated as a p-dopedchannel region) between the doped regions. Transistor 22 includes a gate26 that is electrically coupled to a word line WL to allow selection andcurrent to flow from a bit line BL to memory cell 10. An array ofprogrammable metallization memory units 20 can be formed on asemiconductor substrate utilizing semiconductor fabrication techniques.

FIG. 5 is a schematic diagram of an illustrative programmablemetallization memory array 30. Memory array 30 includes a plurality ofword lines WL and a plurality of bit lines BL forming a cross-pointarray. At each cross-point a programmable metallization memory cell 10,as described herein, is electrically coupled to word line WL and bitline BL. A select device (not shown) can be at each cross-point or ateach word line WL and bit line BL.

FIG. 6 is a flow diagram of an illustrative method of forming aprogrammable metallization memory cell with an oxide layer. FIGS. 5A-5Care schematic cross-section views of a programmable metallization memorycell with an oxide layer at various stages of manufacture.

At FIG. 7A an ion conductor solid electrolyte layer 16 is deposited onan inert electrode 12 at block 110 of FIG. 6. Both the ion conductorsolid electrolyte layer 16 and the inert electrode 12 can be formedusing known deposition methods such as physical vapor deposition,chemical vapor deposition, electrochemical deposition, molecular beamepitaxy and atomic layer deposition. While not illustrated, the inertelectrode 12 can be deposited on a substrate. The substrate includes,but is not limited to silicon, a mixture of silicon and germanium, andother similar material.

At FIG. 7B a sacrificial metal layer 15 is deposited on the ionconductor solid electrolyte layer 16 at block 120 of FIG. 6. Thesacrificial metal layer 15 can be formed using known deposition methods,as described above. The sacrificial metal 15 has a thickness in a rangefrom 0.5 to 50 nanometers or from 1 to 25 nanometers. The sacrificialmetal 15 can be formed of any useful metal that has a more negativestandard electrode potential than the filament forming metal forming theelectrochemically active electrode, described above. The sacrificialmetal 15 has a smaller atomic radius than the filament forming metalforming the electrochemically active electrode. In many embodiments, thefilament forming metal is silver and the sacrificial metal 15 is nickel,chromium or zinc, for example. The sacrificial metal 15 donateselectrons to the filament forming metal to stabilize filaments formed bythe filament forming metal when the programmable metallization memorycell is in the low resistance state. The sacrificial metal layer 15 isdeposited thin enough so it does not participate in the formation of thefilaments formed by the filament forming metal when the programmablemetallization memory cell 10 is in the low resistance state.

At FIG. 7C an electrochemically active electrode 14 is deposited on thesacrificial metal layer 15 at block 130 of FIG. 6. The electrochemicallyactive electrode 14 can be formed using known deposition methods, asdescribed above. Additional metal contact layer(s) can be formed on theelectrochemically active electrode 14. In many embodiments, at least oneinert metal contact layer is deposited on the electrochemically activeelectrode 14 (not shown).

FIG. 8 is a flow diagram of another illustrative method of forming aprogrammable metallization memory cell with an oxide layer. FIGS. 9A-9Bare schematic cross-section views of another programmable metallizationmemory cell with oxide layer at various stages of manufacture.

At FIG. 9A an ion conductor solid electrolyte layer 16 is co-depositedwith sacrificial metal particles 15 on an inert electrode 12 at block210 of FIG. 8. The ion conductor solid electrolyte layer 16 andsacrificial metal particles 15 and the inert electrode 12 can be formedusing known deposition methods such as physical vapor deposition,chemical vapor deposition, electrochemical deposition, molecular beamepitaxy and atomic layer deposition. While not illustrated, the inertelectrode 12 can be deposited on a substrate. The substrate includes,but is not limited to silicon, a mixture of silicon and germanium, andother similar material.

At FIG. 9B illustrates an electrochemically active electrode 14deposited on the co-deposited ion conductor solid electrolyte 16 andsacrificial metal particle 15 layer at block 220 of FIG. 8. Theelectrochemically active electrode 14 can be formed using knowndeposition methods, as described above. Additional metal contactlayer(s) can be formed on the electrochemically active electrode 14. Inmany embodiments, at least one inert metal contact layer is deposited onthe electrochemically active electrode 14 (not shown).

Thus, embodiments of the PROGRAMMABLE RESISTIVE MEMORY CELL WITHSACRIFICIAL METAL are disclosed. The implementations described above andother implementations are within the scope of the following claims. Oneskilled in the art will appreciate that the present disclosure can bepracticed with embodiments other than those disclosed. The disclosedembodiments are presented for purposes of illustration and notlimitation, and the present invention is limited only by the claims thatfollow.

What is claimed is:
 1. A method comprising: co-depositing an ionconductor solid electrolyte layer and a sacrificial metal particles onan inert electrode, the sacrificial metal are distributed in the ionconductor solid electrolyte layer; depositing an electrochemicallyactive electrode on the ion conductor solid electrolyte layer to form aprogrammable metallization memory cell, the electrochemically activeelectrode comprising filament forming metal and the sacrificial metalparticles have a more negative standard electrode potential than thefilament forming metal.
 2. The method of claim 1, wherein thesacrificial metal particles have a smaller atomic radius than thefilament forming metal.
 3. The method of claim 1 wherein the filamentforming metal is silver and the sacrificial metal particles arechromium, nickel or zinc.
 4. The method of claim 1 wherein sacrificialmetal donates electrons to the filament forming metal to stabilizefilaments formed by the filament forming metal, the filamentselectrically connecting the electrochemically active electrode and theinert electrode.
 5. The method of claim 1 wherein the ion conductorsolid electrolyte material comprises a chalcogenide material.
 6. Themethod of claim 1 wherein the filament forming metal is silver and thesacrificial metal particles are chromium or nickel.